1. Field of the Invention
The present invention relates generally to a process for producing hydrogen and, more particularly, to a process for producing high purity hydrogen from a refinery offgas feedstock.
2. Description of Background Art
There are a variety of known processes for producing hydrogen. Some of the more frequently employed processes include steam reforming of natural gas or naphtha, catalytic reforming of hydrocarbons boiling in the range of heavy straight run (HSR) gasoline or heavy oils (e.g., fuel oil), and the partial oxidation of heavy oils or natural gas. Steam reforming of natural gas is perhaps the most widely employed process for producing hydrogen. The cost of natural gas as a feedstock in processes to produce hydrogen is large, when compared to the alternative provided by the process of this invention.
To our knowledge, the use of the refinery offgas described hereinbelow as a feedstock for the production of high purity hydrogen in any currently known process, including those mentioned above, has never been offered. In fact, refinery offgas is characteristically unsuited to function well as a feed in steam or catalytic reforming. In particular, because of the high olefin content of refinery offgas it cannot be fed to a steam reformer, since the activity of the reforming catalyst rapidly becomes spent due to excess coking. Furthermore, due to the low H.sub.2 content and the high N.sub.2 and carbon oxides content of refinery offgas, it is difficult to recover H.sub.2 from an offgas feed. The presence of sulphur, usually in the form of hydrogen sulphide, in offgas feeds can also present a problem, insofar as the added step of removing sulphur from the feed is necessary, since the catalysts used in the known processes for steam reforming are highly sulphursensitive. Similarly, the presence of nitrogen in offgas is problematic since it can be poisonous to some of the hydrogen processing catalysts.
Until now, refinery offgas had very little value and, in fact, imposed a liability on the operator of the refinery, since it must be safely disposed of to comply with environmental regulations due to soot formation by olefins and other unsaturates, such as diolefins and aromatics. Typically, a portion of refinery offgas is used as a supplement fuel to fire the furnaces in a refinery installation and the excess, which is abundant, must be flared. Again, however, because of the high olefin content of refinery offgas, the flame produced can result in undesirable levels of soot.
U.S. Pat. No. 3,545,926 describes a process for generating hydrogen from liquid hydrocarbons by partial oxidation followed by a water gas shift reaction and carbon dioxide removal.
U.S. Pat. No. 3,874,592 describes a burner for the partial oxidation of hydrocarbons to synthesis gas.
Accordingly, a constructive and profitable use of refinery offgas, which, at the same time, eliminates the need for its safe disposal, provides a remarkable advantage to those skilled in the art.